The U.S. Environmental Protection Agency provides assistance to states in conducting surveys of indoor 222Rn. Alabama, Kentucky, Tennessee, Wisconsin, and Wyoming completed statistically designed surveys during the 1986-1987 heating season. In all states, probability-based samples of 5800 houses were tested using charcoal canisters exposed for 48 h. Thus, sample results can be validly extrapolated to the target population of all owner-occupied, ground-level houses having listed telephone numbers. Estimates of population parameters (e.g., median) and their associated confidence intervals are given for each state, for geographic regions within states, and for basement and nonbasement houses. Results confirm that 222Rn concentration varies widely from one state to another and from one geographic region to another within a state; however, the same pattern of differences was not evident in basement or nonbasement houses. Short-term 222Rn readings appear to follow a log-normal distribution.